Generally, an LCD device displays a picture image by controlling light transmittance of a liquid crystal using an electric field.
To this end, the LCD device includes a liquid crystal panel arranged in a matrix arrangement and a driving circuit for driving the liquid crystal panel.
The liquid crystal panel is provided with pixel electrodes and a common electrode to apply the electric field to each of liquid crystal cells.
The pixel electrodes are formed on a lower substrate in a liquid crystal cell while the common electrode is formed on an entire surface of an upper substrate in a single body. Each of the pixel electrodes is connected with a thin film transistor (TFT) used as a switching device. The pixel electrodes are driven along with the common electrode in accordance with a data signal supplied through the TFT.
The LCD device can be fabricated to have a smaller size than that of a cathode ray tube, and is widely used for personal computers, notebook computers, office automation machines such as copiers, cellular phones, and pagers.
An active matrix type LCD device employs color filters of red (R), green (G), and blue (B) corresponding to the three primary colors of light to display a range of colors.
The respective color filters are arranged adjacent to one another and a corresponding color signal is applied to each color filter to control brightness, thereby displaying the colors.
The LCD device is fabricated using several processes with a substrate, including washing, substrate manufacture, substrate bonding/liquid crystal injection, and packaging. In the manufacturing process, the color filters are formed on the upper substrate.
Generally, a pigment dispersing method is most widely used to manufacture each color filter. In the pigment dispersing method, the color filter is manufactured by coating, exposure, development, and firing after dispersing pigment into a polyimide or acryl resin material of the color filter.
The pigment dispersing method has an advantage in that it is easy to form a fine pattern of the color filter. However, the pigment dispersing method has a drawback in that the manufacturing process of the color filter is complicated because a photolithographic process is required for each of the R, G, and B color filters.
FIG. 1 is perspective assembly view illustrating a portion of a general LCD device.
As shown in FIG. 1, upper and lower substrates 10 and 30 oppose each other and they are separated from each other at a constant interval. A liquid crystal layer 50 is interposed between the substrates 10 and 30.
The lower substrate 30 is provided with a plurality of gate lines 32 and a plurality of data lines 34, wherein the gate lines 32 cross the data lines 34. A TFT (T) is formed at each crossing point where the gate lines 32 cross the data lines 34.
Further, a pixel region (P) is defined by the crossing point and provided with a pixel electrode 46 connected with the TFT.
Meanwhile, although not shown in detail, the TFT includes a gate electrode supplied with a gate voltage, source and drain electrodes supplied with a data voltage, and a channel that controls the On/Off state of the TFT using the difference between the gate voltage and the data voltage.
A color filter layer 12 and a common electrode 16 are sequentially formed on the upper substrate 10.
The color filter layer 12 includes a color filter that transmits light of a specific wavelength band only and a black matrix disposed at the boundary of the color filter to shield light on the pixel region P of the lower substrate 30.
Upper and lower polarizing plates 52 and 54 are respectively disposed on outer surfaces of the upper and lower substrates 10 and 30 to transmit light only parallel with a polarizing shaft. As a separate light source, a back light is arranged below the lower polarizing plate 54.
As described above, the aforementioned LCD device requires color filters of three primary colors of R, G and B to display full colors.
Hereinafter, a related art color filter substrate for an LCD device and a method for manufacturing the same will be described with reference to the accompanying drawings.
FIG. 2A is a plane view illustrating a related art color filter substrate for an LCD device and FIG. 2B is a sectional view taken along line I-I of FIG. 2A.
As shown in FIG. 2A, black matrices 64 and color filter layers 66 are formed. Each of the black matrices 64 surrounds a pixel region P and includes an opening 62. Each of the color filter layers 66 is provided with R, G and B color filters 66a, 66b and 66c that are repeatedly arranged in sequence using the black matrices 64 as the boundaries per color.
As shown in the cross-sectional view of FIG. 2B, subsequently, a common electrode 68 is formed on an entire surface of a substrate 60 including the color filter layers 66.
In other words, as shown in FIG. 2B, the black matrices 64 are formed on a glass substrate 60 and spaced apart from one another at constant intervals. The R, G and B color filters 66a, 66b and 66c are sequentially formed using the black matrices 64 as the boundaries for the color filter layers 66. An overcoat layer 67 and the common electrode 68 are sequentially formed on the entire surface of the substrate 60 including the color filter layers 66.
FIG. 3A to FIG. 3F are sectional views illustrating a related art method for manufacturing a color filter substrate for an LCD device.
As shown in FIG. 3A, a resin material 64a of consisting of a metal thin film, such as chrome, or carbon is deposited on the glass substrate 60 by sputtering.
As shown in FIG. 3B, a photoresist 65 is deposited on the resin material 64a and then patterned by exposing and developing processes to define a black matrix region.
Subsequently, the resin material 64a is selectively patterned using the patterned photoresist 65 as a mask to form the black matrices 64 at constant intervals.
The black matrices 64 are formed to correspond to a corner of a unit pixel and a region where the TFT is formed, and they shield a region having unstable electric field.
In FIG. 3C, an R color resist is deposited on the entire surface of the glass substrate 60 including the black matrices 64. Then, the R color resist is selectively patterned by a photolithographic process to form the R color filter 66a where both ends overlap on the black matrices 64.
In FIG. 3D, a G color resist is deposited on the entire surface of the glass substrate 60 including the R color filter 66a. Subsequently, the G color resist is selectively patterned by the photolithographic process to form the G color filter 66b. 
The G color filter 66b is formed in a pixel adjacent to the R color filter 66a with the black matrix 64 therebetween.
In FIG. 3E, a B color resist is deposited on the entire surface of the glass substrate 60 including the G color filter 66b. Then, the B color resist is selectively patterned by the photolithographic process to form the B color filter 66c. 
The B color filter 66c is formed in a pixel adjacent to the G color filter 66b with the black matrix 64 therebetween. Thus, the color filter layers 66 of R, G and B are completed.
The color filter layers 66 are generally formed in the order of R, G and B.
As shown in FIG. 3F, to protect and planarize the color filter layers 66, a planarization film is deposited on the entire surface of the glass substrate 60 including the color filter layers 66 by spin coating an acryl based resin or polyimide based resin, thereby forming the overcoat layer 67.
Subsequently, indium tin oxide (ITO) is deposited on the overcoat layer 67 by sputtering to form the common electrode 68. The ITO has good transmittivity, good conductivity and excellent thermal stability, and is a preferred material for a transparent electrode.
The common electrode 68 serves to drive the liquid crystal cell along with a pixel electrode formed on a TFT array substrate.
In accordance with the prior art process described above, the color filter substrate including the black matrices 64, the color filter layers 66, the overcoat layer 67, and the common electrode 68 is completed.
For reference, in an in-plane switching (IPS) mode LCD device, since the common electrode is formed on the TFT array substrate, the color filter substrate supports the black matrices, the color filter layers, and the overcoat layer.
However, the aforementioned related art color filter substrate for the LCD and the method for manufacturing the same have several problems.
First, since the black matrices are formed at the boundary of each color filter using either metal such as Cr or black resin, the black matrix manufacturing cost is high. Second, since the overcoat layer is separately formed to planarize the color filters having an uneven step difference due to the intervening black matrices, the process is complicated and the process time becomes long. Finally, if each color filter is formed to overlap the black matrices, it is difficult to obtain satisfactory planarization and optical density.